Dehydrogenation process

ABSTRACT

IN CATALYTIC DEHYDROGENATION OF PARAFFINS, CATALYST ACTIVITY IS MAINTAINED RELATIVELY CONSTANT WITHIN A DESIRED RANGE BY ULILIZING A HYDROGEN SULFIDE POISONED CATLYST OF PLATINUM OR PALLADIUM AND A GROUP I-B METAL AND GRADUALLY REMOVING POISON FROM THE CATALYST DURING THE DEHYDROGENATION REACTION.

United States Patent O1 hoe 3,632,662 Patented Jan. 4, 1972 3,632,662DEHYDROGENATION PROCESS David R. Dyroif, Creve Coeur, and Dennis A.Ruest, St. Louis, Mo., assignors to Monsanto Company, St. Louis, M0. NDrawing. Filed Mar. 26, 1970, Ser. No. 23,053 Int. Cl. C07c 5/20 U.S.Cl. 260-6833 5 Claims ABSTRACT OF THE DISCLOSURE In catalyticdehydrogenation of parafiins, catalyst activity is maintained relativelyconstant within a desired range by utilizing a hydrogen sulfide poisonedcatalyst of platinum or palladium and a Group I-B metal and graduallyremoving poison from the catalyst during the dehydrogenation reaction.

BACKGROUND OF THE INVENTION This invention relates to an improvedprocess for producing mono-olefins by catalytic dehydrogenation ofcorresponding saturated hydrocarbons. More particularly, this inventionrelates to processes for dehydrogenating linear parafiins containingfrom about 6 to 20 carbon atoms to yield corresponding mono-olefinsuseful as intermediates in the production of detergent alkylates and inother applications.

Processes for the dehydrogenation of parafiins in the presence ofcatalysts comprising a noble metal such as platinum or palladiumdeposited on a support such as alumina or silica are well-known. Incontinuous dehydrogenation reactions utilizing such catalysts, only afraction of the paraffins are converted to mono-olefins and, as theprocessing is continued, the proportion of paraflins convertedcontinuously decreases as a result of a continous decline in catalystactivity (resulting from deposition of coke on the catalyst and possiblyother causes) until the degree of conversion achieved is so low as torequire replenishment or regeneration of the catalyst in order to effecteconomical operation. Further, during the early stages of thedehydrogenation reaction when catalyst activity is high, substantialamounts of undesired by-products, e.g., diolefins, triolefins andaromatics are formed in addition to the desired mono-olefins.Substantial increases in the formation of these undesired byproducts areobserved when attempts are made to increase paraflin conversion byincreasing contact time between the parafiins and catalysts, therebylimiting the, use of such techniques as a practical means of increasingmonoolefin production. Thus, it is seen that during the dehydrogenationreaction the catalyst activity varies so that during a substantialportion of the reaction by-product formation is undesirably high orparafiin conversion is undesirably low. Only during a relatively briefportion of a continuous dehydrogenation reaction is catalyst activity atan optimum so as to produce acceptable conversion of the paraffin withminimum formation of undesired byproducts.

SUMMARY OF THE INVENTION It is an object of this invention to provideimproved processes for continuous catalytic dehydrogenation of paraffinsto yield corresponding mono-olefins characterized by an extended periodof optimized catalyst activity providing an acceptable degree ofconversion with minimum concurrent production of undesired by-products.

Basically, the invention involves poisoning the catalyst to reduce thecatalytic activity thereof so as to obtain desirably high rates ofconversion of parafiins to monoolefins with minimum formation ofby-products, and continuously reducing the degree of poisoning of suchcatalyst to compensate for other factors such as coke deposition whichnormally results in a decline in catalyst activity, thereby maintainingthe catalyst activity relatively constant Within the desired range. Theinvention will be better understood from the following description ofthe preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the process of thisinvention, saturated hydrocarbons are dehydrogenated to thecorresponding mono-olefins by contacting such hydrocarbons underdehydrogenation conditions with a catalyst comprising a noble metal ornoble metal oxide deposited on an inert support, such catalyst beingpoisoned by a quantity of poison sufficient to substantially reduce thedehydrogenation activity thereof and gradually removing the poison fromthe' dehydrogenation catalyst during the dehydrogenation reaction.

Although the process of this invention can be advantageously employed toeffect dehydrogenation of any saturated hydrocarbon, it is particularlyuseful in conjunction with the dehydrogenation of linear paraffinscontaining from 6 to 20 carbon atoms, preferably 9 to 15 carbon atoms,to yield mono-olefins useful as intermediates in the formation ofdetergent alkylates.

Any catalyst of the type comprising noble metals, e.g., platinum orpalladium, deposited on inert supports, e.g., alumina or silica, such asare commonly employed in dehydrogenation reactions can be utilized inthe practice of this invention. Desirably, the catalyst can be nonacidin character, and, to this end, may contain from about 0.01 to 10% byWeight alkali metal in the catalyst support. Various metallic modifierssuch as copper, silver, or iron may, in some instances, beadvantageously employed. A particularly preferred catalyst is onecomprising from about 0.002% to 50% by weight of a Group I-B metal(preferably copper) or metal oxide (preferably copper oxide) or mixturesof such metals and/or oxides and from about 0.005% to 5% of a noblemetal or noble metal oxide of the platinum or palladium families ormixtures thereof, deposited on an alumina support having a surface areaof at least 10 square meters per gram, a macropore volume of at least0.05 cc. per gram and an acidity factor not in excess of 2. I

The acidity factor is determined by placing the alumina support materialprior to the time that any metal or metal oxide has been deposited uponits surface in a reactor at a temperature of 435 C. to 440 C. whilepassing through the reactor and into contact with the alumina ahydrocarbon mixture of 92 weight percent n-dodecane and 8 weight percentn-a-dodecene admixed with hydrogen in a mole ratio of 2 parts hydrogento one part hydrocarbon mixture. The hydrocarbon-hydrogen mixture shouldbe passed oved the alumina base under a pressure of one atmosphere -2pounds per square inch and at a space velocity of 4.65 'LHSV. Thehydrocarbon mixture after being passed over the alumina support materialis then passed through a gas chromatograph in which the chromatographiccolumn is packed with a substrate for separating the mixture accordingto boiling point and polarity. 1% by weight AgNO plus 18% by weightCarbowax 20M polyethylene glycol on Chromasorb W diatomaceous earth is asuitable and preferred substrate. The numerical value of the weightpercent material, based on the total weight of the hydrocarbon mixtureintroduced to the column, which is eluted from the column prior ton-dodecane represents the acidity factor as this term is employedherein. As previously mentioned, the acidity factor should be notgreater than 2.0 and preferably not in excess of 1.0.

The term macropore volume refers to the total volume of pores having aradius greater than 350 A per unit weight of alumina and is measuredusing an Aminco-Winslow mercury porosimeter, model -7107 (AmericanInstrument Company), or equivalent apparatus to determine the internalvolume penetrated between 0 to 2500 p.s.i.g.

Catalyst of this type and other catalysts suitable for use in thisinvention and the use of such catalysts in dehydrogenation reactions aredescribed in detail in U.S. patent application Ser. No. 715,133 filedMar. 22, 1968 and U.S. patent application Ser. No. 860,418 filed Sept.23, 1969, both of said applications copending herewith and having acommon assignee and in U.S. Pats. Nos. 3,432,- 567; 3,312,734;3,435,090; 3,315,008; 3,315,007; and 3,274,287, the disclosures of theforegoing applications and patents being incorporated herein byreference.

In the process of this invention, the poisons used in conjunction withthe foregoing catalysts must not only be capable of reducing thedehydrogenation activity of the catalyst, but must also be removablefrom the catalyst under normal dehydrogenation conditions. (Completeremovability of poison is not necessary, but at least 25% of the poisonshould be removable to provide the desired advantages.) Catalyst poisonssuitable for use in conjunction with selected catalysts of the foregoingtypes include hydrogen sulfide; carbon disulfide; organic amines (thisterm being limited to organic compounds containing 1 or more aminefunctional groups in combination with saturated or unsaturatedhydrocarbon groups but containing no other functional groups) such asaniline, Z-amino pyridine, pyrrolidine, and hexamethylene diamine;mercaptans (this term being limited to organic compounds containing oneor more -SH groups in combination with various saturated or unsaturatedhydrocarbon groups, but containing no other functional groups) such asthiophenol or l-dodecanethiole; organic sulfides (this term is used todefine organic sulfur compounds other than thiophene derivativescontaining a -S group or groups in combination with various saturated orunsaturated hydrocarbon groups but having no other functional groupspresent) such as thioanisole and; compounds containing thiophene and/orthiazole moieties such as thiophene, benzothiophene, and benzothiazole.In the case of the particularly preferred CuPt promoted catalystsdescribed above, the use of hydrogen sulfide as a poison is particularlypreferred. With regard to the organic sulfur containing compounds, it isobserved that as the molecular weight of a particular class of poisonsincreases, the rapidity with 4 which the poison is removed from thecatalyst under normal dehydrogenation conditions decreases.

Poisoning of the catalyst is effected simply by contacting the catalystwith the poison. A particularly convenient technique is to introduce thepoison into a stream of paraffins to be dehydrogenated and contact thepoison laden paraffins with the catalyst under dehydrogenationconditions. In the case of gaseous poisons, e.g., H 8, anotherconvenient technique is to introduce the poison mixed with hydrogen as acarrier. Since passing a paraflin stream in contact with poisonedcatalyst under dehydrogenation con ditions gradually removes poison fromthe catalyst, the concentration of poison in the paraffin stream must besufficiently high to deposit poison at a rate exceeding the rate ofpoison removal. When the dehydrogenation activity of the catalyst hasbeen reduced to the desired level, the poison content of the paraffinfeed stream is eliminated (or reduced as hereinafter explained).

The dehydrogenation conditions in terms of temperature, pressure,relative feed rates and catalyst volume, etc., are conventional andselected in accordance with considerations well understood by thoseskilled in the art of catalytic dehydrogenation. During thedehydrogenation reaction, poison is gradually removed from the catalyst,tending to increase the dehydrogenation activity thereof. This effect,however, tends to be counter-balanced by a normal gradual decline incatalyst activity resulting, for example, from deposition of coke on thecatalyst. Thus, in the process of this invention, these counter-effectsmaintain catalyst activity in a relatively narrow range until most ofthe poison is removed from the catalyst, after which the catalystactivity declines in a normal manner until replacement or regenerationis required.

Preferably, the catalyst activity can be maintained within a relativelynarrow range by selecting a catalystpoison combination such that therate of poison removal under given dehydrogenation conditionscorresponds to the normal rate of decline in catalyst activity.Alternatively, when the combination of poison-catalyst-dehydrogenationconditions is such that poison is removed more rapidly than required tocompensate for normal catalyst activity decline; poison can beintroduced into the paraffin feed to reduce the rate of poison removalfrom the catalyst.

The practice of the invention is further illustrated by the followingexamples.

EXAMPLES I-XlV Six grams of catalyst l0+l4 U.S. standard sieve size andcomprising 2% copper and 0.45% platinum (by weight) deposited on analumina support having an acidity factor of 0.1 (contains about 0.3%sodium in combined form), a macropore volume of about 0.18 cc. per gram,and a surface area of about square meters per gram are used in each ofExamples IXlV. In each example, the catalyst is maintained as a fixedbed in a flow-through dehydrogenation reactor at a temperature of about452 C. The catalyst is poisoned by feeding 50 grams of benzenecontaining the amount of poison (shown as percent by weight S or N)indicated in Table 1 below. Linear dodecane is fed through the reactoralong with some hydrogen for 6 hours, the ratio of catalyst weight ingrams to dodecane fioW rate in moles per hour being 5.7 gm. hr./mo'le.The ratio of hydrogen to hydrocarbon in the reactor is 2, and thereactor pressure is 4 p.s.i.g. The product is analyzed by gas-liquidchromatography and the results are reported in Table 1. No calibrationor correction is applied to the GLC peak areas, so that the indicatedpercentages are relative only. However, this method is appliedconsistently to all runs and thus comparisons among runs are valid.

TABLE 1 Percent dodccane converted to Mono-olefin Poison in yield asbenzene is Lighter Diolefins, percent of Percent N hydrotriolefins.Monoparaffins Example Poison or percent S carbons aromatics olefinsconverted None 0.99 4.7 18.8 76.9 Thiophene 0.1 0. 09 1. 7 12. 4 87. 3Benzothiophene 0.1 0.06 1. 2 10. 1 88. 6 Benzothiazole- 0. 1 0.03 0. 78.6 02. 3 Thioanisole--- 0. 1 0. 07 1. 3 10. 7 88.9 Thiophenol. 0. 1 0.06 1. 1 10. 4 89. 9 l-dodecanethiol 0. 1 0. 07 1. 2 10.8 89.3 VIIICarbon disulfide 0.1 0.06 1.2 11.1 90.0 IX Hydrogen sulfide... 0.10.08 1. 2 11. 3 90. 3 Y Oninnline 1. 0. 16 3. 1 18. 3 85. 0 X 1.0 0.122.1 17.3 88.7 1. 0 0. 24 3. 6 19. 6 83. 6 1. 0 0. 21 3. 1 18. 9 85. 2 IVHexamethylenediamine 1.0 0.08 0. 9 13. 2 92. 0

It is seen from the foregoing examples that the use of catalyst poisonsin accordance with this invention substantially improves catalyticdehydrogenation of paraflins.

What is claimed is:

1. In a continuous process of preparing linear mono olefins having chainlengths of from 6 to 20 carbon atoms by contacting corresponding linearparaffins under dehydrogenation conditions with a dehydrogenationcatalyst comprising from 0.002% to 50% by weight of a first metalliccomponent selected from the group consisting of Group IB metals, oxidesthereof, and mixtures thereof and from 0.005% to by weight of a secondmetallic component selected from the group consisting of platinum,palladium, oxides thereof and mixtures thereof deposited on the surfaceof an alumina catalyst support material having an acidity factor not inexcess of 2.0, a macropore volume of at least 0.05 cubic centimeters pergram and a surface area of at least 10 square meters per gram theimprovement wherein said catalyst is poisoned with a dehydrogenationactivity reducing quantity of poison selected from the group consistingof hydrogen sulfide, carbon disulfide, mercaptans, organic sulfides,compounds containing thiophene moieties, compounds containing thiozolemoieties, and organic amines, and further comprising the step ofgradually removing said poison from the dehydrogenation catalyst duringthe dehydrogenation reaction.

References Cited UNITED STATES PATENTS 2,131,089 9/1938 Beeck et a1.260683.3 3,439,061 4/1969 Henderson et a1. 260-6833 2,604,438 7/1952Bannerot 260-6833 3,067,130 12/1962 Baldwin, Jr., et a1. 260683.33,274,287 9/1966 Moore et a1. 260683.3 3,291,855 12/1966 Haensel260683.3 3,437,585 4/1969 Kuchar 260--683.3

DELBERT E. GANTZ, Primary Examiner V. OKEEFE. Assistant Examiner 5:3 3 IUNITED STATES PATENT OFFICE- QERTIFICATE OF CORRECTION patent 3,632,652Dated January 4', 1972 Inventor g) Davld Dyroff and D n-T118 A. Ruest Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 6, line 25, the word "portion" should-be poison Signed and sealedthis 13th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOTTSGHALK -r uztesting OfficerCommissioner of Petents

